Can I perform PWM Dimming using LinkSwitch-PH

Posted by: lbaerd on 11/15/2010

I have designed an LED driver using LinkSwitch-PH and it works great. I understand that Linkswitch-PH is Triac Dimmable. However, I would need my design to be PWM dimmable. I will have a microcontroller to control the dimming preferably using PWM. Is there any work around that could be done on the current LinkSwitch-PH design.

I have read the latest datasheet of LinkSwitch-PH and there seems to be new device part number LNK41xEG. I have quoted a sentence from page 3 of the datasheet:
"For non-dimming or PWM dimming applications with LNK413-419, the external resistor should be a 24.9 kOhm ±1%, for high line and universal input voltage designs, and 49.9 kOhm ±1% for low line input voltage designs."

Does it means that LNK41xEG allow PWM Dimming. Is that a new part?

Thanks alot

Comments

Yes you can. You can do this in 2 ways (Also see attachment)
1) Analog way - in which a PWM signal is generated then filtered to achieve an equivalent FB pin current and this current is injected to the FB pin to control the output current
2) Digital way - where the PWM signal is used to switch the device on and off to achieve PWM dimming. When PWM signal is high a transistor connects BP pin to RFB pin thereby inhibiting switching, and when PWM signal is low, BP pin is disconnected from FB pin and a DC bias current flows into the FB pin to turn on the Linkswitch-PH and deliver the programmed constant output current

Thanks for your reply. That's very helpful of you. In fact I had tried out something similar to the 1st method mentioned. However, I have limited dimming range. When I start to control the LED current to very dim, the LinkSwitch enter into autorestart mode. I guess maybe the 2nd method will give better dimming range.

I just begin to think if I could manipulate the Voltage Monitor pin to perform dimming. I could tie 49.9k resistor to the Reference pin and start manipulating the current into the Voltage Monitor pin to control the output current. Does this allow me to have wide dimming range?

Thanks

I also want to use 419 as dimmable driver through PWM signal. Pls send the circuit diagram.

Hi Vijay,

Thank you very much for choosing Power Integrations.

You can use DER-263 as reference circuit for your application. This design makes use of Linkswitch-PH.

https://led-driver.power.com/design-support/reference-designs/design-examples/der-263-14-w-pwm-analog-dimmable-led/

Power Integrations also has a transformer design tool you can use to design your transformer. You can find the tool on the link below:

https://led-driver.power.com/design-support/pi-expert/

Power